1. Field of the Invention
This invention relates to methods of preparing opto-electronic devices such as photovoltaic (PV), photodetector, and organic light emitting diode (OLED) devices, in particular to methods to produce a large surface area interface between two functional layers of materials in these devices, such that each of the two layers of materials has a continuous non-tortuous exciton or electron/hole charge percolation path from the interface to its other surface without the presence of islands of material from one layer within the material of the other layer.
2. Related Technology
In opto-electronic devices such as PV and OLED devices, functional layers are sandwiched between an anode layer, generally of indium tin oxide (ITO) on a glass or polymer substrate, and a low work-function cathode layer such as aluminium/lithium fluoride. The functional layers include an electroluminescent or light-absorbing layer, and may include a hole transport layer and/or an electron transport layer. In these devices, charge carriers (electrons or holes) are transported to or from the electroluminescent or light-absorbing layer through a hole transport layer and/or an electron transport layer, from or to the cathode and anode layers. More specifically, charge carriers injected into an electroluminescent layer or generated by a light-absorbing layer will travel to or from the interface between the light-active layer and a hole transport layer or an electron transport layer, from or towards the relevant electrode at the other surface of the hole transport layer or an electron transport layer.
In general, the functional materials are deposited as layers over one electrode on a substrate, and the cell is completed by depositing the other electrode over the functional layers. Bi-layers of organic materials have been used for PV applications, for example a bi-layer of a light absorbing layer over a hole transporting layer. However, the bi-layer structure, in which the interface between the two layers is essentially planar, results in low quantum efficiencies, due to the small interfacial area existing between the two functional organic materials, and the mismatch between the typical exciton range and the thickness of polymer required to absorb most of the light.
Polymer blends have been used for organic PV and OLED applications. However, the blended structure, in which the two functional materials of the blend exist as separate but interdispersed phases, can also result in low quantum efficiencies despite the large interfacial contact between the two phases, due to the structure presenting long, tortuous percolation paths for exciton or electron/hole charges to travel to their collecting or source electrodes.
It would therefore be desirable to produce, in an opto-electronic device such as an organic PV device or an OLED device, an interface between bi-phasic functional layer materials that can provide not only an increased interfacial area compared with a bi-layered structure, but that also can present a shorter, less tortuous charge percolation path compared with a blended structure.